A multiple access manner refers to a manner in which simultaneous access of multiple user terminals is implemented on a specified radio resource. Common multiple access manners include manners such as time-division multiple access (English: Time-Division Multiple Access, TDMA for short), frequency-division multiple access (English: Frequency-Division Multiple Access, FDMA for short), code-division multiple access (English: Code-Division Multiple Access, CDMA for short), and orthogonal frequency-division multiple access (English: Orthogonal Frequency-Division Multiple Access, OFDMA for short).
Constellation expansion multiple access (English: Constellation Expansion Multiple Access, CEMA for short) is an access manner in which dam streams of multiple users are transmitted non-orthogonally and simultaneously in particular time and frequency domains by using a feature of higher-order constellation expansion. Specifically, a step for transmitting a signal between a user terminal and a base station device by using a constellation expansion multiple access technology includes:
For downlink data streams that need to be sent by a base station device to multiple user terminals, channel coding and random scrambling processing are separately performed on these downlink data streams, to obtain an information bit corresponding to each downlink data stream. Further, a transmission symbol corresponding to each information bit is determined. Obtained transmission symbols are superimposed, to form a higher-order transmission symbol, and the higher-order transmission symbol is transmitted to a user terminal by using a transmit antenna.
After receiving the higher-order transmission symbol, the user terminal performs balancing on the received higher-order transmission symbol according to a minimum mean square error criterion, and obtains, by means of soft demodulation, the downlink data streams sent by the base station device to the user terminal.
At present, for the constellation expansion multiple access manner, it is proposed that different error control levels on a same frequency are implemented by using a two-layer constellation expansion mode. It is also proposed that different channel coding is used for different users, and amplitude and phase adjustment is performed, to implement simultaneous transmission by multiple users. It is also proposed that in an independent modulation method for different modulation layer levels, a modulation symbol of each layer is superimposed based on reliability, and different users use different modulation layer levels in constellation expansion, and the like. However, in the currently proposed constellation expansion multiple access manner, when multi-user access is implemented by means of constellation expansion, the following problems still exist:
1. In a multi-user state, a problem that the constellation expansion does not match an antenna gain easily occurs in the current constellation expansion multiple access manner.
2. In a multi-user state, interference between data streams is relatively serious in the current constellation expansion multiple access manner, and therefore, signal transmission quality cannot be ensured.